Tubular sausage casings based on regenerated cellulose having an internal reinforcement of fiber paper in particular of hemp fiber paper, have long been known (see G. Effenberger, Wursthüllen-Kunstdarm [Sausage casings—artificial skin], 3rd edition [2006] Deutscher Fachverlag GmbH, Frankfurt a.M., pp. 47-55). These casings, generally termed cellulose fiber skins are generally produced by the viscose process. In this process first a fiber paper is formed to give a tube having overlapping longitudinal edges which is charged with viscose from the outside, from the inside or from both sides using a ring die. The viscose is then regenerated to cellulose hydrate in a precipitation bath.
Cellulose fiber skins may also be produced by the newer amine oxide process. In this process the cellulose is dissolved in aqueous amine oxide, preferably in N-methylmorpholine N-oxide monohydrate. This solution is applied to the fiber paper formed to give a tube. The cellulose is then precipitated in a bath which contains a dilute aqueous amine oxide solution. In this manner a seamless casing may be obtained, as in the viscose process. In contrast to the viscose process, the cellulose in the amine oxide process is not chemically derivatized, but is purely physically dissolved. After stuffing with sausage emulsion, cellulose fiber skins are substantially transparent.
However, all of these processes have the disadvantage that they are highly cost intensive. In addition, the diameter of the casing, that is to say the “caliber”, is predetermined by the diameter of the ring gap of the ring die, in such a manner that, on a plant, only one caliber can be produced in each case per die used. A change to a different caliber is therefore associated each time with an alteration and corresponding down time of the plant.
In addition, acrylic- and/or polyvinylidene chloride (PVDC)-coated textile skins (U.S. Pat. No. 4,525,418=DE-A 31 47 519, DE-A 37 04 563, U.S. Pat. Nos. 5,043,194, 5,744,251 and 5,364,674) are also known. The textile base material used therein can be a consolidated nonwoven, a spunbonded nonwoven or a woven fabric made of natural fibers and/or artificial fibers. Fibers which are mentioned are those of cotton, linen, wool, silk, cellulose esters, regenerated cellulose, polyester, polyamide, polyacrylonitrile, polypropylene and poly(vinyl chloride). The base material is coated with an acrylic emulsion polymer based on lipophilic esters of (meth)acrylic acid with lower alkanols, in particular butyl acrylate. The coating is applied using conventional coating devices, such as an air knife, roll doctor or rubber cloth doctor, in a direct process or in the transfer process. Subsequently the coated strip is formed to give a tube and the seam is closed by gluing, stitching, sealing or welding. By an appropriate choice of the coating, the acrylic-coated textile skin can be made water vapor-permeable and gas-permeable and it is smokable, so that it is also suitable for long-life sausage.
In DE 10 2005 056 574 which was unpublished at the priority date of the present application, a food casing made of a flat fibrous material coated on one or both sides with acrylic resin is disclosed. The casing can also be tubular and have a glued longitudinal seam as shown in the examples. The seam in this case is generated using a hotmelt glue. There are no further details on the type of hotmelt glue.
Suitable glues based on polyurethane were disclosed in US 2003/0050423 A1 and US 2006/0247326 A1.
It is further well known in the art to apply an outermost coating of polyvinylidene chloride (“PVDC”) or polyvinyl chloride (“PVC”) on the side of the casing facing away from the food to impart water and oxygen barrier properties.
However, the above mentioned casings have some disadvantages. Firstly incomplete coatings owing to lack of adhesion of the hot melt glue to the acrylic used constantly occur. In addition, a casing has different properties in the region of the longitudinal seam produced by a polyamide or conventional PUR hotmelt than in the remaining regions, in particular different elasticity, extensibility and smoke as permeability. The strength of the longitudinal seam frequently weakens under the action of hot water, as is customary in use of the casing for scalded-emulsion or cooked meat sausages. In general, casings having glued seams based on conventional hotmelts have insufficient strength for the increased requirements of modern industrial sausage manufacture, for example automated boiling lines, so that here increased amounts of rejects occur which, in particular, are caused by bursting of the seam.
Applicants have determined that the seam bursts within conventional glued casings because the glue line has a lower extensibility than the casing material, inter alia. During stuffing the casing material is usually extended by 5%. This leads to tensions at the cohesive surface or interface between the coated textile and the glue. Little breakages can occur, resulting in the formation of small tunnels through which sausage emulsion can leak out. In this case, the casing loses its barrier properties. This compromises hygiene in the production due to mold formation along the seam. It might also change the sausage properties. Both are regarded as absolutely unacceptable. Furthermore, the seam can break easily at the cohesive surface between PVDC barrier coatings and the glue.
The machine speed in sausage factories increased during the last decade, hence the conditions of producing the sausage became more drastic. For today's requirements concerning strength and extension, the region of the seam is a weak-point. The seam-line bursts more often during cooking than before and liquid from the sausage emulsion leaks out through adhesion surfaces. Thus the performance of the glue line continues to be a critical point in the overall success of the casing.